Environmental Monitoring

Leachate Collection & Management

When water comes into contact with the waste, it releases the chemicals and particles within it, and the resulting mixture is known as “leachate.” Leachate can contain harmful chemicals, and, if not captured and managed properly, can percolate through the soil and contaminate the groundwater.


The Asotin County Regional Landfill (ACRL) has engineered bottom liner and leachate management systems in the modern landfill footprint (Cells A-D). The liner system, made up of different synthetic materials of plastics and clay products, along with natural compacted soils, is designed to hold leachate within the confines of the landfill. The leachate collection system, made up of sands/gravels and pipes, collects and drains leachate to a single low-point in the cell bottom, known as a sump. Leachate drains from the sump in pipes to a lift station, where it is pumped to the sewer line and conveyed to the City of Clarkston’s Wastewater Treatment Plant.

Typical Landfill Bottom Cross Section

Future Final Capping System

Eventually, when the landfill cells are full and can no longer accept waste, they will be covered by a similar liner system as the one found at the bottom of the cells. The purpose of covering a landfill, also known as capping a landfill, is to keep as much water away from the waste as possible, in order to minimize the production of leachate. Landfill covers also help to contain landfill gas for collection and management.

Landfill Gas Control & Monitoring

As organic waste degrades, methane as well as other gases, such as carbon dioxide and hydrogen sulfide, are generated by natural microorganisms. These gases are air pollutants and are harmful to the environment. At the Asotin County Regional Landfill (ACRL), landfill gas is pulled from the waste with vacuum suction and then sent to a burner system called a flare station, to be destroyed.


Gases are monitored at probes, located around the landfill footprint and in structures, to check for gas migration. Gas migration is when gases diffuse into the soil surrounding the landfill, oftentimes due to a breach in the liner system. Gas collection lines are placed in the landfill, as waste is buried, and connected to the active collection system. These gases are monitored at active collection stations, located on the south edge of the landfill. Using a special instrument, gas flow rate and characteristics (methane, carbon dioxide, and oxygen content) are checked and recorded. If necessary, gas flows are adjusted with valves that open and close the collection lines, before being sent to the flare station.

Gas Monitoring Station
Water Monitoring Station

Groundwater Monitoring

As another means of environmental protection, groundwater is routinely monitored at the Asotin County Regional Landfill (ACRL) to detect potential leaks in the bottom liner system. Groundwater is monitored using a series of wells. Wells are placed upstream and downstream of groundwater flow. The groundwater is monitored before reaching the landfill (upgradient) and after passing beneath the landfill (downgradient), and the samples are compared to see if any harmful chemicals have been introduced by a possible leak in the bottom liner system.

Groundwater Monitoring Well